1. Field of the Invention
The present invention relates to sealed contactors, and particularly to low cost sealed contactors in hermetically sealed housings.
2. Description of the Related Art
Hermetically sealed contactors are magnetically-operated devices used for repeatedly establishing and interrupting an electrical power circuit and for switching of high electrical currents and/or high voltages. They typically have fixed and movable internal contacts, and an internal actuating mechanism supported within a hermetically sealed housing. In one type of contactor, air is removed from the contactor housing to create a vacuum that suppresses arc formation, provides long operating life and allows for low resistance operation of the contactor. In another type of contactor, the evacuated chamber can be backfilled under pressure with an insulating gas, which allows the contactor to operate with good arc-suppressing properties.
One type of conventional contactor has moving components housed within a ceramic housing. These types of contactors can operate with a vacuum formed in the housing or with the housing having internal pressure from an injected gas. This allows the contactors to operate with higher voltage and/or lower resistance characteristics and ceramic housings also allow the contactors to operate at high temperature. Ceramic housings, however, can be expensive and difficult to manufacture. Contactors may also comprise a housing with a ceramic header. Ceramic headers offer many of the same voltage, resistance and/or temperature characteristics of ceramic housings as well as offering a means whereby contacts can be electrically isolated from one another. Traditional ceramic headers can be difficult and expensive to manufacture because they are complex shapes that require special tooling, difficult metallization, and time consuming post processes.
Current hermetically sealed contactors also have housings that are complex shapes of ceramic or are epoxy sealed plastic. Epoxy sealed housings can be more prone to failure at high temperature and the all-ceramic envelope products can be very expensive. While the use of flat ceramic can be used, one problem is that the arc chamber is separate from the header. During high current interrupt, arc plasma could reach other metal parts outside the arc chamber if it is not properly sealed. To properly seal the chamber, epoxy or a brazement could be used, however they must be exact solutions dimensionally and can reduce the performance and/or increase the price.
Additionally, conventional contactors have a movable plunger component that is driven by a solenoid in order to move the movable contacts to the stationary contact. Sealed solenoid driven contactors can be problematic due to pressure build-up on one side of the plunger during plunger travel. This imbalance of pressure slows plunger movement and can reduce solenoid performance. To address this, some relays are provided with a bigger gap in the plunger to reduce the magnetic force or they will machine in expensive grooves to allow gas to flow by the outside of the plunger as the plunger moves to the stationary contacts.
Another operating characteristic of conventional contactors is the performance parameter release time, which is how fast the plunger and its movable contactor can open and break from the stationary contacts, thereby breaking the current being carried. To achieve this, strong springs are traditionally used to move the armature when the coil power is removed. Having strong springs requires a large amount of coil power to operate the contactor. The efficiency of the magnetic field increases as the relay operates and as a result the holding power required is much less than the power required to begin operation. The steady state power can be reduced by using a two coil design, one high power coil for operating the relay, and a lower power coil for holding the armature in place after operation. However, traditional two coil designs can be costly and/or can be problematic due to power-reducing components often comprise mechanical switches that are located outside of the contactor. This can expose the components to the hazards of the external environment, which can reduce the efficiency and life of the contactor.
Also, in a typical single pull single throw solenoid plunger contactor, the solenoid moves the moveable contact a certain distance before it makes contact with the stationary contacts. This distance is known as the contact gap, and provides the electrical isolation to stop current flow. The magnetic force from the solenoid has an exponential rise as it approaches the end of its travel. After the moveable contact makes contact with the stationary contact, the plunger continues to move often referred to as overtravel. This overtravel compressing a single contact spring, often referred to as the overtravel spring. The compression force of this spring is applied to the contacts and the greater the spring for the better the electrical performance. However, the spring force can be greater than the solenoid force, which can cause the solenoid actuator to stall as it is moving and fail to close.
U.S. Pat. No. 4,039,984 to DeLucia et al. generally discloses a high-voltage magnetic contactor enclosed within a housing of insulating material which contains a gas, such as sulfur hexafluoride. The terminals within the housing extend through its wall and are secured to and sealed to the housing to prevent gas from leaking from the housing. Leads are connected to the terminals externally of the housing, with insulating material surrounding the leads and being secured by the terminals to the housing. An operating mechanism within the housing shifts a pivoted arm electrically connected to one of the terminals within the housing into and from contact with another of the terminals within the housing. The housing is made from a material that has high impact strength and high heat resistance such as a polyamide or polycarbonate resins.
U.S. Pat. No. 4,168,480 to DeLucia discloses a high voltage magnetic contactor that is enclosed by an insulating housing containing a gas, such as sulfur hexafluoride, under pressure. The switch terminals removably extend through a wall of the housing and are sealed. The magnet contactor structure is removably connected to the housing by a sealed joint. A fill valve extends through a wall of the housing and is sealed to the housing. The armature shifts a pivotal arm in the housing between open and closed contact positions. The housing is formed of a polyamide material that is resistant to deterioration by fluorine gas, the material being poly hexamethylene terephthalic amide.
U.S. Pat. No. 5,554,963 to Johler et al. discloses a contactor that includes a plastic enclosure, contacts disposed in the plastic enclosure for selectively operating to make and/or break at least one electrical connection, a gas filling containing at least one electronegative gas, and a sealed plastic encapsulation for preventing the at least one electronegative gas from diffusing away. The electronegative gases are not utilized at high pressure, but under atmospheric pressure or slightly higher pressure. Since normal pressure is used, a hermetically sealed encapsulation can be dispensed with and the enclosure can be made of low-cost plastics without connection to the outside air.
U.S. Pat. No. 6,265,955 to Molyneux et al. generally discloses a contactor having a primary external sidewall formed by a plastic potting cup with a sealed chamber arranged within the cup and having the contactor's moving components. The cup is enclosed at the bottom by a base, with the base and cup serving as a mold to hold epoxy material poured into the cup and cured to provide a hermetic seal. Insulated electrical leads extend through the epoxy material from the sealed chamber for connection of fixed and movable contacts to external circuitry. The base can have a threaded portion that extends from the underside of cup. The potting cup is preferably formed of Nylon 6/6.